A greenhouse gas (GHG) is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process by which radiative energy leaving a planetary surface is absorbed by some atmospheric gases is called the greenhouse effect.[1] The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone.[2]

In the Solar System, the atmospheres of Venus, Mars, and Titan also contain gases that cause greenhouse effects. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth's surface would be on average about 33°C (59°F)[3][4][5]

Power plants largest source of GHGs in US

U.S. power plants released 72 percent of the greenhouse gases reported to the EPA for 2010, according to federal data that was the first catalog of global warming pollution by facility. The data include more than 6,700 of the largest industrial sources of greenhouse gases, or about 80 percent of total U.S. emissions.[7]

While comprehensive, the EPA registry is not complete: it does not include carbon dioxide and other greenhouse pollution from motor vehicles or agribusiness. According to Think Progress, the exclusion of industrial agriculture pollution is due to a loophole inserted by the House of Representatives. However, the EPA will require emissions reporting from additional industry groups for 2011 data, including petroleum and natural gas systems, industrial wastewater treatment, electronic manufacturing, and industrial waste landfills.[8]

GHG emissions from US federal lands

A 2012 report by Stratus Consulting and commissioned by The Wilderness Society found that 23 percent of total U.S. greenhouse gas emissions come from oil, gas, and coal extracted from federal lands and waters. Approximately 44% of coal, 36% of crude oil, and 18% of natural gas produced in the U.S. are extracted from public lands.[9]

In 2011, the group Sightline calculated the carbon dioxide emissions from U.S. coal exports versus Alberta's tar sands, and found projected emissions from coal exports to be substantially higher (the estimate did not count the emissions associated with mining, transport, construction, or any other related activities, nor any non-CO2 or fugitive emissions, to allow for a more simple, straightforward comparison.)

Coal exports: The calculation assumed that 110 million tons of Powder River Basin coal are exported each year, consistent with the 60 million tons planned for the Millennium Bulk Logistics Longview Terminal and the 50 million for Gateway Pacific Terminal at Cherry Point, Washington (this is probably a low estimate: Longview project sponsors have been found using an 80 million ton figure, and there are talks of other Coal exports from ports on the west coast of Canada and the United States, such as Grays Harbor, Washington; St. Helens, Oregon; and Coos Bay, Oregon.) The estimate assumed that Powder River Basin coal generates 8,500 BTUs per pound, and that one million BTUs would produce 212.7 pounds of CO2, consistent with U.S. Department of Energy figures. The final calculation was 199 million tons of CO2 per year in “direct” emissions from the coal exports

Tar sands: To calculate the CO2 emissions from the Keystone XL Pipeline, it was assumed that the pipeline moved 830,000 barrels of oil per day, in line with U.S. State Department figures, working out to about 303 million barrels per year. It was then assumed that each barrel of oil contains 0.43 metric tons of C02, which the U.S. EPA assigns for an “average” barrel of oil (direct emissions from burning are the same regardless if it's oil or tar sands), which works out to about 144 million short tons of CO2 per year for direct emissions from burning the oil. To account for the particular crudeness of tar sands oil, the emissions that are associated with extracting and processing it for use were factored using figures from David Strahan, Wikipedia, and other sources; it was assumed that extracting the oil and “upgrading” to make it suitable for refining results in somewhere around 18 to 26 percent more carbon emissions than the direct emissions from burning the fuel itself. A mid-point of that range, 21.7 percent, was used, and added up to 31 million tons of CO2, for a combined direct and indirect emissions total of 175 million short tons of CO2 per year for the pipeline oil.[10]

In the ruling, the Court said that the EPA Administrator must determine whether or not there was sufficient scientific evidence to support the statement "that emissions of greenhouse gases from new motor vehicles cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare... The Supreme Court decision resulted from a petition for rulemaking under section 202(a) filed by more than a dozen environmental, renewable energy, and other organizations." (Section 202(a) of the Clean Air Act is titled "Emission standards for new motor vehicles or new motor vehicle engines.")[12]

In May 2007, President George W. Bush issued an executive order, the Clear Skies Initiative, proposing regulations on greenhouse gases weaker than those proposed by the EPA itself following the court order.[13] The American Clean Energy and Security Act in the form that it passed the US House of Representatives would strip the authority from EPA under the Clean Air Act to regulate green house gasses.[14]

April 2009: EPA declares greenhouse gases a threat to public health and welfare

On April 17, 2009 the EPA issued a “proposed endangerment finding” and a related proposed “cause or contribute finding” regarding greenhouse gases under section 202(a) of the Clean Air Act (section dealing with “Emission standards for new motor vehicles or new motor vehicle engines”). The EPA held a 60-day public comment period for these proposed findings, and received over 380,000 public comments. On December 7, 2009, the EPA issued two final findings regarding greenhouse gases under section 202(a) of the Clean Air Act: Endangerment Finding – The Administrator finds that the current and projected concentrations of the six key well-mixed greenhouse gases--carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6)--in the atmosphere threaten the public health and welfare of current and future generations. Cause or Contribute Finding – The Administrator finds that the combined emissions of these well-mixed greenhouse gases from new motor vehicles and new motor vehicle engines contribute to the greenhouse gas pollution which threatens public health and welfare.[15][16][17]

December 2009: EPA finalizes endangerment finding

On December 7, 2009, EPA finalized its endangerment finding that greenhouse gases including carbon dioxide are a threat to human health and welfare. The announcement was the final step in the April 2007 Supreme Court ruling in Massachusetts v. EPA, which found that under the Clean Air Act, the EPA must regulate greenhouse gas emissions if they endanger public health and welfare. The EPA's decision paves the way for new regulation of emissions from power plants, factories, and automobiles. Announced on the first day of international climate talks at COP15 in Copenhagen, the move gives President Obama new regulatory powers that could help gain consensus in efforts to curb global warming. Both Obama and EPA Administrator Lisa Jackson have said they prefer climate change legislation as a means of regulating global warming pollution, but the finding provides an alternative means of establishing emissions limits if the legislation fails.[18][19] On December 15, 2009, the final findings were published in the Federal Register under docket ID [EPA-HQ-OAR-2009-0171; FRL-9091-8]. Further information on the findings may be found on the EPA website: http://epa.gov/climatechange/endangerment.html

March 2010: EPA Waits for 2013 to regulate carbon emissions from 50,000 to 75,000 tons a year

On March 3, 2010 EPA Administrator Lisa Jackson told the Senate Appropriations panel reviewing EPA's budget that the agency would focus on large polluters spewing more than 75,000 tons a year. “It will probably be at least two years before we would look at something like, say, a 50,000 threshold,” Jackson said. The initial phase of greenhouse-gas rules will go into effect in 2011 said Jackson.[20]

Senator John D. Rockefeller IV (D) of West Virginia on March 4, 2010 introduced legislation that would delay the EPA's carbon rules. The bill calls for a "two-year suspension" that will give Congress “the time it needs to address an issue as complicated and expansive as our energy future." Two House Democrats, West Virginia’s Nick Rahall and Virginia’s Rick Boucher, also introduced legislation that would put EPA's greenhouse gas regulations for so-called “stationary sources” on hold for two years. Rep. Rahall was co-author of the cap-and-trade bill that passed the House in June 2009 and would replace EPA direct regulation on carbon emissions.[21]

June 2010: Murkowski resolution to overturn EPA finding defeated

On June 10, 2010, a resolution by Alaska Senator Lisa Murkowski - a "Resolution of Disapproval" to overturn the EPA's endangerment finding on carbon pollution - was defeated in the Senate by a vote of 53-47. Every one of the Senate's 41 Republicans voted in favor of it, along with six Democrats: Mary Landrieu (La.), Blanche Lincoln (Ark.), Mark Pryor (Ark.), Ben Nelson (N.D.), Evan Bayh (Ind.), and Jay Rockefeller (W.Va.). The resolution would have overturned the EPA's finding that carbon pollution is a threat to public health and welfare.[22]

December 2010: EPA issues plan to regulate power plants and petroleum refineries

On December 23, 2010, the EPA issued its plan for establishing greenhouse gas (GHG) pollution standards under the Clean Air Act in 2011. The agency looked at a number of sectors and is moving forward on GHG standards for fossil fuel power plants and petroleum refineries—two of the largest industrial sources, representing nearly 40 percent of the GHG pollution in the United States. Under the plan, EPA will propose standards for power plants in July 2011 and for refineries in December 2011 and will issue final standards in May 2012 and November 2012, respectively. EPA will accept public comment on the plans for 30 days following publication of notice in the Federal Register.[23]

The EPA regulation addresses existing sources, using the statutes of the Clean Air Act's New Source Performance Standards (NSPS) to impose limits in 2012 on the amount of CO2 the biggest polluters can emit. The EPA said it would cover 40 percent of U.S. emissions.[24].

The EPA has also been developing a permitting program for new (or substantially upgraded) sources. In May 2010, the EPA issued its "Tailoring Rule," determining which sources will need to get permits (very large sources). In November 2010, it issued "PSD and Title V Permitting Guidance for Greenhouse Gases," which detailed that the permitting program would be run much like existing permitting programs: through the states.[25]

The regulations will be applied to plants that were "grandfathered" (exempted) under the original Clean Air Act.[25]

Feb. 2011: House votes to block EPA regulation of GHGs

On Feb. 18, 2011, the Republican-controlled House voted to block the Environmental Protection Agency from regulating greenhouse gases. The 249-177 vote added the regulation ban to a spending bill that would fund the government through Sept. 30, 2011. Texas Republican Ted Poe pressed the anti-EPA measure. His Texas district is home to many oil refineries.[26]

On March 3, 2011, Senator James Inhofe, Republican of Oklahoma, and Representative Fred Upton, Republican of Michigan, formally introduced the “Energy Tax Prevention Act,” a bill that they said would reverse the EPA’s finding that carbon dioxide and other heat-trapping greenhouse gases are a danger to human health and the environment. According to Inhofe: “The Energy Tax Prevention Act stops cap-and-trade regulations from taking effect once and for all." The bill has 42 co-sponsors in the Senate, all Republicans. In the House, three Democrats joined Upton and his Republican co-sponsors - Nick Rahall of West Virginia, Dan Boren of Oklahoma and Collin Peterson of Minnesota, reportedly to protect key industries in their states – coal, oil and agriculture – that would be affected by greenhouse gas regulations.[27]

The Inhofe-Upton bill allows many Clean Air Act programs to continue, but takes away the agency’s authority to apply the landmark law to carbon dioxide. A deal negotiated with automakers to limit carbon dioxide emissions from cars and light trucks would be allowed to stand through 2016, but no further greenhouse gas emissions rules for vehicles would be permitted. State programs to try to address global warming and carbon emissions would be allowed to continue.[27]

September 2011: Delay announced

On Sep. 14, 2011, the EPA said it will miss an end-of-month target for proposing greenhouse gas regulations for power plants.[28]

March 2012: Rule for new plants

On March 27, 2012, the EPA released its new rule limiting CO2 emissions from future electricity generating plants in the U.S. The EPA is proposing that new plants emit no more than about 454 kilograms of CO2 per megawatt‐hour, and would go into effect in 2013. It would have the biggest impact on coal-fired plants, but would not apply to existing plants or those already under construction. The EPA did leave the door open for companies that want to build new coal plants by allowing utilities to phase-in CO2 controls like carbon capture and storage over decades, as long as the plant's 30-year average of emissions met the new standard.[29]

Science reported that the cap is unlikely to have much impact on current U.S. energy-industry practices, as utilities are favoring new power plants fueled by natural gas. (The average U.S. natural gas plant emits 800 to 850 pounds of carbon dioxide per megawatt, while coal plants emit an average of 1,768 pounds of carbon dioxide per megawatt.) According to Science: "Nearly all gas-fired power plants built in the U.S. since 2005 would already meet the standard, according to EPA, as would typical gas plants on the drawing boards. So, in practice, analysts say the new standard will probably result in few—if any—immediate changes in how utilities build or operate new power plants."[29]

September 2013: revised rule

On Sep 20, 2013, the EPA issued new CO2 rules separating coal and gas regulations. Newly built coal-fired power plants will have to keep carbon emissions below 1,100 pounds per megawatt hour—a level that will force new plants to have carbon capture and storage technology. Newly constructed natural-gas plants will be permitted to emit no more than 1,000 pounds of C02 per megawatt hour - essentially the level at which cleaner burning natural-gas plants currently perform.[30]